Cellular radio systems use fixed base station transceivers, which are typically mounted on buildings or towers. These base station transceivers transmit and receive radio signals from wireless mobile units (also known as subscriber units). Because these base station transceivers are fixed, changing an initial deployment location is usually performed at considerable expense. Therefore, the initial layout or placement of such base station transceivers plays a fundamental role in determining both the performance and profitability of any cellular system layout. Assigning too few base station transceivers to a given area results in blocked call attempts, increased interference levels, and service outage holes; assigning too many base station transceivers to a given area increases system costs substantially, thereby decreasing profitability. As such, the determination of the correct base station transceiver placement and density is an important step in the design of any cellular system.
In the past, a common method for base station transceiver layout begins with selecting demographic information, such as census data for regions (e.g., a zip code or similar defined region of interest) within a given service area. The population for each region is then multiplied by an appropriate scale factor in order to determine the offered load in Erlangs (one Erlang is equal to one full hour of phone use or conversation per hour of clocktime or 1 call minute per minute) for that subregion. These offered loads are then used to assign base station transceivers within each subregion.
The problem with this method of assigning offered load based on fixed demographic information is that it fails to account for the dynamic nature of the users. In essence, it assumes that the population described by the demographic database remain in their homes. In practice, however, large percentages of the population travel to and from their places of employment or recreation during the daytime hours, which are the peak demand hours for cellular traffic. In addition, those persons remaining at home typically use their standard wireline phones for conducting conversations rather than paying the "per minute" charges associated with cellular calls. As such, base station transceiver layout based on standard census information typically overpredicts offered load within residential areas and typically underpredicts offered load within commercial areas and along main transportation arteries.
Thus it should be apparent that there is a need for an improved method and system for distributing offered load that eliminates the error introduced by designing a communications system based upon static data that represents users in their home.